G1: I can talk to people on my phone but I can't hear them on headpiece. Only speaker works. How do I repair speaker in headpiece?

it seems to be an hardware fault.since as you said you cant hear the caller, your phones headpiece is seemed to be faulty. you need to replace it form a nearest service center.also before that just try pressing the up arrow key on you phone while calling it may increase the volume if you accidentally decreased the headpiece volume.
good luck

im unable to hear others voice on calls...except on speaker phone..could come one solve this??

this gets to be a common problem for cell phones...

try having a software flash, if nothing happens you can use bluetooth or a headpiece, or you can purchase a new phone

maybe if it is under warranty you will get a free or reduced replacement

This would be a mic not a spear my friend you need to have this replaced or ship the phone back to the carrier for a replacment I do know most carriers have this insurence and you must have it if you have a g1 at least I would. This sounds like another Tmobile phone gone bad and it would be in your best interest to have it replaced. You als may want to check and see if you did not mute the mic accidently.

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/edwy_1a56970cf1ea4620

All of a sudden, while on a phone call using my g1, the in-call sound stopped working and now only works when on speaker. Can someone please help me with this?

Well first of, there is your warranty, but if your phone breaks after expirations, there is both an T-Mobile G1 Repair Guide and a third party T-Mobile G1 Repair Service, so there is no need to worry.

More then likey you will have to perform a master reset to the device

Buying a new one would be very expensive. Go Visit HTC Repair Center located in Dallas Tx if you are local. If you are outside Dallas you can Mail-in your Phone to them.
For more information on HTC G1 Repair visit www.drcellphone.com. They are the best Cell Phone Repair Service Center in the Nation.

The speaker of your cellphone is broken.
You must visit the store you bought it from to fix it for you.
Probably it will need to be replaced by a new one.

Thank you

I had same problem with my PPC so I tried hard reset didn't help, PCS support did hard reset and nothing, same problem so what I did is insert that headset plug in and out couple of times that fix the problem but any time I use my wired headset problem comes back.
I realized that the problem was in the 2.5 jack it self, I took it to Sprint store, left it for a hour when I am back the tech guy said that they replace my phone with new one, oh well this is third phone in less then 14 mos.
But anyway now it works just fine so I try to use Bluetooth headpiece much is possible. Waiting for my 2 year contract to end so I can get PPC-6800 or something better, had too many problems with this phone. I like the phone but it was freezing up on me every day and tech support didn't do s!#@!#t for me to fix it until this problem comes up, I'm kind of glad it did :-) in the way.

If you need further help, reach me via phone at https://www.6ya.com/expert/toly_4d7df273bdf34d91